JP4719570B2 - Liquid state detection sensor - Google Patents

Description

  The present invention relates to a liquid state detection sensor including a liquid property detection element for detecting at least the concentration of a specific component in a liquid stored in a liquid storage container.

  In recent years, for example, a NOx selective reduction catalyst (SCR) may be used in an exhaust gas purification device that reduces nitrogen oxide (NOx) discharged from a diesel vehicle to a harmless gas, and an aqueous urea solution is used as the reducing agent. . It is known that this aqueous urea solution has an appropriate concentration range (the concentration range of urea contained in the aqueous urea solution) for effectively reducing nitrogen oxides. However, even when a urea aqueous solution having an appropriate concentration is accommodated in the urea water tank, the urea concentration may deviate from an appropriate range due to a change with time. Further, there is a possibility that liquid (for example, pure water) other than the appropriate urea aqueous solution is erroneously stored in the urea water tank. Therefore, a concentration sensor that detects the concentration of the urea aqueous solution is attached to the urea water tank, and a warning is issued in the event of an abnormality such as when the concentration of the urea aqueous solution deviates from the appropriate range. There has been proposed a system that informs the driver that it is no longer possible (see, for example, Patent Document 1).

  Further, as a sensor for detecting the urea concentration contained in the urea aqueous solution, a sensor in which a sensor part is attached to the front end part of a support part in which a urea water tank attachment part is formed at the rear end part is known ( For example, see Patent Document 2). In this patent document 2, the sensor part is comprised from the density | concentration detection part containing a heat generating body, and the heat transfer member for density | concentration detection parts for heat exchange with urea aqueous solution, and surrounds the heat transfer member for density | concentration detection parts. Thus, a cover member that forms the urea solution introduction path is provided. By providing the cover member in this manner, it is difficult for the aqueous urea solution around the sensor unit to vigorously flow due to vibration or the like, and it is possible to improve the accuracy of concentration detection by the sensor unit.

JP 2000-371831 A JP-A-2005-84026

  However, since the concentration sensor disclosed in Patent Document 2 is configured to be mounted using a plurality of mounting screws when mounting the cover member, the number of parts tends to increase and the assembly work is complicated, and the structure itself is complicated. Become.

  The present invention has been made in view of such problems, and there is no problem in assembly in a liquid state detection sensor including a liquid property detection element for detecting at least the concentration of a specific component in a liquid. It is an object of the present invention to provide a liquid state detection sensor in which a structure for attaching an enclosing member to a holder that holds a property detection element in a state in which a tip end portion is protruded is not complicated.

The present invention according to claim 1 is a liquid state detection sensor including a liquid property detection element for detecting at least the concentration of a specific component in a liquid stored in a storage container.
A holder that holds the liquid property detection element in a state in which the tip of the liquid property detection element protrudes from its tip, a holder attachment member that supports the liquid property detection element by attaching the holder,
An enclosing member formed with a flow hole through which the liquid flows, and is attached to the front end portion or a portion near the front end of the holder so as to surround the front end portion of the liquid property detecting element. ,
The holder has a recess formed on the outer peripheral surface of the distal end portion or a portion near the distal end, while the surrounding member protrudes inward to a proximal end portion or a proximal end portion fitted on the holder. A convex part that can be fitted into the concave part by elastic deformation is provided, the convex part is fitted into the concave part, and the surrounding member is attached to the holder in a retaining shape , and the enclosure A support member that is made of rubber and has a ring shape so as to straddle a portion corresponding to the convex portion of the outer peripheral surface of the member and a portion of the outer peripheral surface of the holder where the surrounding member is not externally fitted. It is characterized by being attached to the outer peripheral surfaces of the surrounding member and the holder in an interference fit.

  According to a second aspect of the present invention, the convex portion is formed by raising the wall of the surrounding member itself so that the end portion of the convex portion itself is positioned on the tip side and protrudes obliquely inward. It is a protrusion piece part, It is a liquid state detection sensor of Claim 1 characterized by the above-mentioned.

In the first aspect of the present invention, as described above, a portion of the outer peripheral surface of the surrounding member corresponding to the convex portion and a portion of the outer peripheral surface of the holder where the surrounding member is not externally fitted. A liquid state detection sensor including , as a technical matter , a rubber-made support member that is ring-shaped and attached to the outer peripheral surface of the surrounding member and the holder in an interference-fitted manner. It is.

The present invention described in claim 3 is a liquid state detection sensor including a liquid property detection element for detecting at least the concentration of a specific component in a liquid stored in a storage container,
A cylindrical first member extending in the longitudinal direction;
A cylindrical or solid second member that is disposed inside the first member and extends along the longitudinal direction of the first member;
Holding the liquid property detection element in a state where the tip of the liquid property detection element protrudes from its own tip, and a holder attached to the tip of the second member;
A flow hole through which the liquid flows is formed, and an enclosing member covering a radial periphery of the tip portion of the liquid property detection element protruding from the tip of the holder,
The holder has a recess formed on the outer peripheral surface of the distal end portion or a portion near the distal end, while the surrounding member protrudes inward to a proximal end portion or a proximal end portion fitted on the holder. It is provided with a convex part that can be fitted into the concave part by elastic deformation, the convex part is fitted into the concave part, and the surrounding member is attached to the holder in a retaining shape,
Between the outer side of the second member and the inner side of the first member, a rubber-made support member that supports the second member with respect to the first member is interposed, and the support The member straddles the surrounding member and the surrounding member so as to straddle the portion corresponding to the convex portion of the outer peripheral surface of the surrounding member and the portion of the outer peripheral surface of the holder where the surrounding member is not externally fitted. It is characterized by being attached to the outer peripheral surface of the holder in an interference fit.

According to a fourth aspect of the present invention, the convex portion is formed by raising the wall of the surrounding member itself so that the end portion of the convex portion itself is positioned on the tip side and protrudes obliquely inward. It is a protrusion piece part, It is a liquid state detection sensor of Claim 3 characterized by the above-mentioned.

The present invention according to claim 5 is the liquid state detection sensor according to any one of claim 3 or claim 4 , wherein the tip end portion of the first member extends around the radial direction of the surrounding member. The liquid state detection sensor is extended to a covering position.

The present invention according to claim 6 is the liquid state detection sensor according to any one of claims 3 to 5 , wherein the first member is an outer cylindrical electrode made of a conductor, The second member is an internal electrode made of a conductor, and the first member and the second member form a level detection unit that changes in capacitance according to the level of the liquid stored in the storage container. This is a liquid state detection sensor.

  The liquid state detection sensor according to claim 1 is provided with the surrounding member as described above, and the holder is formed with a concave portion on the outer peripheral surface of the distal end portion or a portion closer to the distal end. The base end portion or the proximal end portion that is externally fitted to the holder is provided with a convex portion that can be fitted into the concave portion by projecting inward and elastically deforming. Thus, the surrounding member can be attached to the holder in a retaining manner simply by elastically deforming the convex portion by fitting the surrounding member into the holder and pushing it into the concave portion. . Such an encircling member corresponds to the cover member in Patent Document 2, but is attached in a retaining shape by pushing in itself when attached. That is, according to the present invention, the surrounding member can be simply and quickly attached only by pushing it in without causing a complicated structure and without requiring another member such as a screw member. For this reason, the man-hour for fixing the surrounding member is greatly reduced as compared with the conventional one, the assembly is facilitated, and the configuration is simplified, so that an inexpensive liquid state detection sensor can be obtained.

  Furthermore, in the present invention, since the liquid property detecting element is surrounded by the surrounding member, the surrounding member acts as a barrier and protects the liquid property detecting element even if the liquid in the storage container flows vigorously due to vibration or the like. Therefore, it is possible to reduce the pressure accompanying the flow from directly reaching the liquid property detecting element. As a result, the durability of the liquid property detecting element can be improved, and the liquid surrounding the liquid property detecting element is not vigorously replaced, so that stable concentration detection can be performed.

  The liquid property detection element (hereinafter also simply referred to as element) and the liquid state detection sensor may be any sensor that detects at least the concentration of a specific component contained in the liquid. In addition to the concentration, the temperature of the liquid and the lower limit of the liquid You may detect whether it fell below the level. Examples of the liquid include an aqueous urea solution, a solution or slurry containing metal powder or ceramic powder, and the specific component contained in the liquid may be urea as long as it is an aqueous urea solution.

  The convex portion may be a dowel shape or a protrusion, as long as the surrounding member can be attached to the holder in a retaining manner by elastically deforming the convex portion and fitting the convex portion into the concave portion. The shape and structure are not particularly limited. However, as in the second aspect, the wall of the surrounding member itself is arranged so that the end portion (tip portion) of the convex portion itself is located on the tip side (tip side of the element) and protrudes obliquely inward. In the projecting piece formed by cutting and raising, when the surrounding member is formed by press forming a metal plate, it is easy to form the convex portion, and when it is attached to the holder, the protruding portion is high. Stopping property can be imparted. In addition, what is necessary is just to set the number of a recessed part and a convex part suitably.

Furthermore, as described in claim 1, the outer peripheral surface of the surrounding member extends over a portion corresponding to the convex portion and a portion of the outer peripheral surface of the holder where the surrounding member is not externally fitted. The ring-shaped support member made of rubber is attached to the outer peripheral surface of the surrounding member and the holder in an interference fit , so that the surrounding member is loosely fitted to the holder (clearance gap). Even if it is fitted, the mounting can be stabilized without rattling. That is, in consideration of the accuracy of the fitting portion, the surrounding member is preferably fitted with a gap, but in that case, the attachment becomes unstable due to looseness. However, if the support member is attached in this way, the surrounding member can be firmly fixed, and thus the attachment with high stability or high reliability can be obtained. That is, according to the present invention, the durability is enhanced even in a usage environment that is constantly subjected to vibration, such as when mounted on an automobile.

The invention described in claim 3, based on its configuration, the mounting of the enclosing member, and the effect of the post-mounting obtain the same effect as in claim 1. According to a third aspect of the present invention, in place of the holder mounting member according to the first aspect, a holder is attached to the tip of the second member corresponding thereto, and the second member extends in the longitudinal direction. A rubber-made support that is arranged inside one member and that supports the second member with respect to the first member between the outside of the second member and the inside of the first member. A member is interposed. For this reason, in addition to the effect similar to that in claim 1, the effect of stabilizing the support of the second member is also obtained. Moreover, the support member straddles a portion corresponding to the convex portion of the outer peripheral surface of the surrounding member and a portion of the outer peripheral surface of the holder where the surrounding member is not externally fitted, Since it is attached to the outer peripheral surfaces of the surrounding member and the holder in an interference fit, the attachment of the surrounding member is also stable.

Further, according to the liquid state detection sensor of the present invention, the second member is elastically supported on the inner side of the first member by the rubber support member. Generation | occurrence | production of resonance etc. can be suppressed and a deformation | transformation of a 1st member and a 2nd member can be suppressed effectively. Accordingly, the holder can be stably supported by the support member, and as a result, the holding of the liquid property detection element by the holder can be favorably maintained over a long period of time. Furthermore, in the invention described in claim 4, the same effect as that of the invention described in claim 2 can be obtained.

Further, as described in claim 5, in the case where the tip end portion of the first member is extended to a position covering the circumference of the surrounding member in the radial direction, the periphery of the liquid property detecting element is added to the surrounding member. Is also covered at the tip of the first member. For this reason, even if the liquid in the storage container flows violently due to vibration or the like, the front end portion of the surrounding member and the first member serves as a barrier, so that the pressure accompanying the flow directly reaches the liquid property detection element. This can be further reduced. As a result, the durability of the liquid property detecting element can be further improved, and the liquid surrounding the liquid property detecting element is not vigorously replaced, so that more stable concentration detection can be performed.

Furthermore, in the invention described in claim 6 , the first member and the second member are made of conductors, and the first member and the second member are used to electrostatically change the level of the liquid stored in the storage container. A level detector (that is, a capacitor) in which the capacitance changes is formed. In this way, by using the first member and the second member for disposing the liquid property detection element at the target position in the container as the level detection unit, a single liquid state detection sensor is used, so that at least the liquid state is detected. It is possible to detect the concentration of the specific component and the change in the level of the liquid. Thereby, even when it is necessary to detect the concentration of the liquid stored in the storage container and to detect the level change, both detections can be performed by attaching only one sensor. When the liquid exhibits conductivity like an aqueous urea solution, the surface of the portion of the second member that is to come into contact with the liquid in order to prevent a short circuit between the first member and the second member. By coating with an insulating film, it is possible to detect a level change of the conductive liquid.

  Hereinafter, an embodiment of a liquid state detection sensor embodying the present invention will be described with reference to the drawings. With reference to FIGS. 1-12, the structure of the liquid state detection sensor 100 as an example is demonstrated.

  FIG. 1 is a longitudinal front view of the liquid state detection sensor 100. FIG. 2 is an enlarged cross-sectional view in the vicinity of the liquid property detection unit 30 of the liquid state detection sensor 100 and a further enlarged view of the main part. FIG. 3 is a schematic diagram showing the heater pattern 115 of the ceramic heater 110. FIG. 4 is a perspective view of the holder 120 that protrudes and holds the tip of the ceramic heater 110 as viewed from the tip side, and a perspective view of the protector 130 attached thereto as viewed from the tip side. FIG. 5 is a cutaway front view of the state in which the holder 120 that holds the tip of the ceramic heater 110 protruding is attached to the internal electrode 20, and a cutaway front view of the protector 130 attached thereto. FIG. 6 is a cutaway front view of the state in which the protector 130 is externally fitted to and attached to the distal end portion of the holder 120 in FIG. 7 is a cross-sectional view taken along line X1-X1 in FIG. FIG. 8 is a perspective view of the rubber bush 80 as viewed obliquely from below. FIG. 9 is a side view of the rubber bush 80. FIG. 10 is a plan view of the rubber bush 80. FIG. 11 is a cross-sectional view of the rubber bush 80 as viewed from the direction of the arrows along the one-dot chain line AA in FIG. FIG. 12 is a bottom view of the liquid state detection sensor 100 when the liquid state detection sensor 100 shown in FIG. 1 is viewed in the direction of the axis O from the front end side. In the liquid state detection sensor 100, the longitudinal direction of the level detection unit 70 (capacitor composed of the outer cylinder electrode 10 and the internal electrode 20) is the axis O direction, and the side where the liquid property detection unit 30 is provided is the tip side, The side on which the mounting portion 40 is provided is the rear end side.

The liquid state detection sensor 100 of the present embodiment includes a state of an aqueous urea solution used for reduction of nitrogen oxide (NOx) contained in exhaust gas of a diesel vehicle, that is, the level (liquid level) of the aqueous urea solution, It is a sensor for detecting the concentration of urea as a specific component contained in the urea aqueous solution. As shown in FIG. 1, a liquid state detection sensor (hereinafter also simply referred to as a sensor) 100 includes an outer cylinder electrode 10 having a cylindrical shape, and the direction of the axis O of the outer cylinder electrode 10 inside the outer cylinder electrode 10. A level detector 70 composed of a cylindrical internal electrode 20 provided along the line, a liquid property detector 30 provided on the distal end side of the internal electrode 20, and a liquid state detection sensor 100 are accommodated in an aqueous urea solution. It is comprised so that it may explain in full detail below from the attaching part 40 etc. for attaching to the urea water tank (not shown) as a container. In addition, the outer cylinder electrode 10 in this embodiment is a cylindrical first member extending in the longitudinal direction according to the third aspect of the present invention, and the internal electrode 20 is disposed inside the first member. A cylindrical or solid second member that is disposed and extends along the longitudinal direction of the first member. Here, the internal electrode 20 constitutes a holder mounting member according to the first aspect of the present invention.

  The outer cylinder electrode 10 constituting the sensor 100 in this embodiment is made of a metal material and has a long and thin cylindrical shape extending in the axis O direction. A plurality of narrow slits 15 are intermittently opened along each bus bar on three bus bars that are equally spaced in the circumferential direction on the outer periphery of the outer cylindrical electrode 10. Further, at the distal end portion 11 of the outer cylinder electrode 10, on each bus bar in which the slit 15 is formed, it is interposed between the inner electrode 20 to be described later and is used for preventing the rubber bush 80, which forms a support member, from coming off. Each opening 16 is provided. Furthermore, one air vent hole 19 is formed on a bus bar different from each bus bar in which the slits 15 are formed at a position close to the base end portion 12 on the rear end side of the outer cylinder electrode 10. Further, the distal end portion 11 of the outer cylinder electrode 10 is further distal to the axial O direction from the position of the opening portion 16 so as to surround the protector 130 that forms an enclosing member that covers and protects the periphery of the ceramic heater 110 described later in the radial direction. Has been extended. And the most advanced part is opened, The protector 130 which comprises the liquid property detection part 30 is in the state which can be visually recognized from the opening side (FIG. 1 lower side). As described above, the outer cylinder electrode 10 corresponds to the “first member” in the present invention.

  Next, the outer cylinder electrode 10 is welded in a state in which the base end portion 12 is engaged with the outer periphery of the electrode support portion 41 of the metal attachment portion 40. The attachment portion 40 functions as a base for fixing the liquid state detection sensor 100 to the urea water tank (not shown), and an attachment hole (not shown) for inserting the attachment bolt is formed in the flange portion 42. Further, on the opposite side of the electrode support portion 41 with the flange portion 42 of the mounting portion 40 interposed therebetween, a relay is provided for electrical connection between the liquid state detection sensor 100 and an external circuit (not shown). A housing portion 43 for housing the circuit board 60 and the like is formed.

  The circuit board 60 is placed on a board placement portion (not shown) protruding from the four corners of the inner wall surface of the housing portion 43. The accommodating portion 43 is covered and protected by a cover 45, and the cover 45 is fixed to the flange portion 42. Further, a connector 62 is fixed to the side surface of the cover 45, and a connection terminal (not shown) of the connector 62 and a pattern on the circuit board 60 are connected by a wiring cable 61. The circuit board 60 and an external circuit (not shown) are connected via the connector 62.

  A hole 46 penetrating into the accommodating portion 43 is opened in the electrode support portion 41 of the attachment portion 40, and the base end portion 22 of the internal electrode 20 is inserted into the hole 46. The internal electrode 20 of the present embodiment is made of a long and thin cylindrical metal material extending in the direction of the axis O. On the outer peripheral surface of the internal electrode 20, an insulating film 23 made of a fluorine resin such as PTFE, PFA, ETFE, an epoxy resin, a polyimide resin, or the like is formed. The insulating coating 23 is formed in the form of a resin coating layer by applying such a resin on the outer surface of the internal electrode 20 by dipping or electrostatic powder coating and heat-treating it. As will be described later, a level detector 70 is formed between the internal electrode 20 and the outer cylinder electrode 10 by forming a capacitor whose capacitance changes according to the level of the urea aqueous solution. As described above, the internal electrode 20 corresponds to the “second member” in the present invention.

  A flange-shaped pipe guide 55 is fixed to the outer periphery of the base end portion 22 on the rear end side in the axis O direction of the internal electrode 20 to fix the internal electrode 20 to the mounting portion 40. 41 is disposed inside a cylindrical inner case 50 that is disposed with the upper end engaged in a hole 46 in 41, and is engaged via a pipe guide 55. That is, the pipe guide 55 is an annular guide member joined to the end edge of the base end portion 22 of the internal electrode 20. On the other hand, the inner case 50 is a flanged cylindrical resin member that positions and supports the internal electrode 20 so that the internal electrode 20 and the outer cylindrical electrode 10 are reliably insulated, and the tip side is an electrode support portion of the mounting portion 40. 41 is inserted into the hole 46. The inner case 50 is formed with a flange portion 51 that protrudes radially outward. When the inner case 50 is engaged with the electrode support portion 41, the electrode support portion is inserted from the housing portion 43 side. 41 is inserted through the hole 46. The flange 51 is brought into contact with the bottom surface of the housing 43 to prevent the inner case 50 from passing through the hole 46. Further, the internal electrode 20 is inserted into the inner case 50 from the accommodating portion 43 side, but the pipe guide 55 is brought into contact with the flange portion 51 so that the inner electrode 20 is prevented from falling off from the inner case 50.

  Further, an O-ring 53 and an O-ring 54 are provided on the outer periphery and the inner periphery of the inner case 50, respectively. The O-ring 53 seals a gap between the outer periphery of the inner case 50 and the hole 46 of the mounting portion 40, and the O-ring 54 is formed between the inner periphery of the inner case 50 and the outer periphery of the base end portion 22 of the internal electrode 20. The gap between them is sealed. Thereby, when the liquid state detection sensor 100 is attached to the top plate or upper lid of the urea water tank (not shown), the water tightness is prevented so that the inside and the outside of the urea water tank do not communicate with each other through the accommodating portion 43. And airtightness is maintained. A plate-like seal member (not shown) is attached to the tip side surface (the lower surface in FIG. 1) of the flange portion 42 of the attachment portion 40, and the flange portion when the liquid state detection sensor 100 is attached to the urea water tank. The watertightness and airtightness between 42 and the urea water tank are maintained.

  As shown in FIG. 1, the pipe guide 55 is pressed against the flange 51 of the inner case 50 by the two pressing plates 56 and 57 as shown in FIG. It depends on. The holding plate 56 is fixed in the housing portion 43 by tightening with a screw 58 with an insulating holding plate 57 sandwiched between the pipe guide 55 and the pipe guide 55 being pressed. Thereby, the internal electrode 20 joined to the pipe guide 55 is fixed to the electrode support portion 41. A hole 59 is opened in the center of the holding plates 56 and 57 used for fixing, and two electrical connections are made between the electrode lead wire 52 of the internal electrode 20 and a ceramic heater 110 described later. A two-core cable 91 containing lead wires 90 (only one lead wire 90 is shown in FIG. 1) is inserted and electrically connected to the pattern on the circuit board 60, respectively. An electrode (not shown) on the ground side of the circuit board 60 is connected to the mounting portion 40, whereby the outer cylinder electrode 10 welded to the mounting portion 40 is configured to be electrically connected to the ground side. ing.

  Next, the liquid property detection unit 30 will be described in detail. The liquid property detection unit 30 is connected to the tip 21 of the internal electrode 20. As shown in FIG. 2 in an enlarged manner, in this embodiment, the liquid property detection unit 30 includes a ceramic heater 110 as a liquid property detection element that detects the concentration of urea in the urea aqueous solution, and the ceramic heater 110. Is held in a state in which the tip portion is protruded, and the periphery of the tip portion of the ceramic heater 110 exposed from the holder 120 and the holder 120 made of an insulating resin attached to the tip portion 21 of the internal electrode 20 is held. And a protector 130 that covers and protects.

  Among these, as shown in FIG. 3, in the ceramic heater 110, a heater pattern 115 mainly composed of Pt is formed on a plate-shaped ceramic base 111 made of an insulating ceramic, and a ceramic base (not shown) forming a pair. The heater pattern 115 is embedded in a state of being sandwiched between. Here, the cross-sectional area of the pattern constituting the heating resistor 114 is made smaller than the pattern of the lead portions 112 and 113 serving as both poles for voltage application, so that heat is generated mainly in the heating resistor 114 during energization. To be done. In addition, via conductors (not shown) penetrating the surface of the ceramic base 111 are provided at both rear ends of the lead portions 112 and 113, and two terminals that relay the connection with the two lead wires 90. 119 (only one of them is shown in FIG. 2) is electrically connected. The ceramic heater 110 corresponds to the “liquid property detecting element” in the present invention.

  Further, as shown in FIGS. 2 and 4 to 6, the holder 120 made of an insulating resin that supports the ceramic heater 110 is concentric and has a large diameter cylindrical portion 122 having a large diameter and a small diameter cylindrical portion having a small diameter. The tip portion 21 of the internal electrode 20 is inserted inside the large-diameter cylindrical portion 122 and covered from the outer periphery thereof. In addition, the outer peripheral surface of the site | part which connects the large diameter cylindrical part 122 and the small diameter cylindrical part 121 in this holder 120 is made into the taper-shaped step part (taper part) 123 which diameter-reduces toward a front-end | tip. In the outer circumferential surface of the small-diameter cylindrical portion 121 that forms a portion closer to the tip of the holder 120, four concave portions 124 are formed (recessed) at a constant depth in the circumferential direction at equal angular intervals in this embodiment. However, the recess 124 is configured to be substantially rectangular in a front view (see FIG. 5). Further, a taper is attached to the outer peripheral portion of the tip (surface) 125 of the small diameter cylindrical portion 121 of the holder 120.

  On the other hand, the inner peripheral surface of the holder 120 is formed in a circular cross section that expands in a stepped shape toward the small diameter cylindrical portion 121, the step portion 123, and the large diameter cylindrical portion 122. However, an opening 126 that forms a rectangle when viewed from the direction of the axis O (in the cross section) is formed at the tip 125 of the small-diameter cylindrical portion 121 so that the tip 110b of the ceramic heater 110 can protrude without any gap (FIG. 2). FIG. 7). The short side and the long side of the rectangle in the cross section of the opening 126 are set so as to correspond to the dimensions of the thickness and width of the ceramic heater 110, respectively. As shown in FIG. 7, the center of each side of the opening 126 is formed so as to correspond to the centers of the four recesses 124 described above in the cross section. In the ceramic heater 110, the lead portions 112 and 113 (see FIG. 3) in the longitudinal direction are inserted into the small-diameter cylindrical portion 121, and the tip portion 110b side in which the heating resistor 114 is embedded extends from the tip 125 of the holder 120. In this state, the ceramic heater 110 is fixed by holding a seal in the opening 126 of the holder 120 by filling and solidifying the adhesive or resin 129 in the inner peripheral surface 127 of the small-diameter cylindrical portion 121. ing.

  On the other hand, the inner diameter of the large-diameter cylindrical portion 122 is configured to be slightly larger than the outer diameter of the tip portion 21 of the internal electrode 20, and two concave grooves 128b are formed on the inner peripheral surface 128 in the circumferential direction in this embodiment. Has been. Thus, when such a holder 120 is externally fitted to the distal end portion 21 of the internal electrode 20 from the large-diameter cylindrical portion 122 side, two concave grooves on the inner peripheral surface 128 of the large-diameter cylindrical portion 122 are provided. A seal between the inner peripheral surface 128 and the outer peripheral surface of the internal electrode 20 is ensured via each seal ring (for example, rubber O-ring packing) 140 loaded in the 128b, and the internal electrode 20 has an internal seal. It is configured to prevent the liquid constituting the measurement object from entering through this interval. Further, an annular shelf step portion 128 c is formed on the inner peripheral surface of the step portion 123 of the holder 120, and when the holder 120 is mounted on the tip portion 21 of the internal electrode 20, The end surface 21b is in contact with the shelf step portion 128c so as to be positioned in the axis O direction. The insulating coating 23 is provided on the outer peripheral surface of the internal electrode 20 from the distal end side to the proximal end portion 22 on the rear end side from the position where the seal ring 140 is disposed at the distal end portion 21 on the distal end side of the internal electrode 20. Even if the level detector 70 is immersed in the urea aqueous solution in the urea water tank (not shown), the internal electrode 20 may be in direct contact with the urea aqueous solution. Not to be.

  Before the holder 120 is mounted, the core wires of the two lead wires 90 of the cable 91 are joined to the terminals 119 of the ceramic heater 110 by caulking or soldering, respectively. Furthermore, the insulating protection member 95 covers and protects the terminal 119 and the lead wire 90 together with the joint portion. The two lead wires 90 are inserted through the cylindrical internal electrode 20 and connected to the circuit board 60.

  Next, the protector 130 that is an enclosing member that covers and protects the periphery of the tip of the ceramic heater 110 that is a liquid property detecting element will be described in detail with reference to FIGS. 2 and 4 to 7. The protector 130 is a protective member for the exposed portion of the heater 110 formed by pressing a metal plate into a bottomed cylindrical shape, for example, and the ridge angle portion between the bottom portion 132 and the body portion 133 is curved. Chamfered and stiffened. In addition, on the outer periphery of the body portion 133 of the protector 130, in the present embodiment, two circulation holes 135 for forming a measurement object are formed on four bus bars that are equally spaced in the circumferential direction. Has been. The bottom portion 132 is formed with a flow hole 136 that is similarly opened at the center thereof. Such a protector 130 is set so that the inner diameter of the body part 133 is the same as or slightly larger than the outer diameter of the small-diameter cylindrical part 121 in the holder 120 described above.

  And the protector 130 is a proximal end (rear end) or a proximal end portion of the body portion 133 that is externally fitted to the holder 120, and is provided at four locations at equal angular intervals in the circumferential direction. By projecting inward and elastically deforming, a convex portion 137 that can be fitted into the concave portion 124 of the holder 120 is provided. The convex portion 137 may be formed to protrude so as to swell in a circular dome shape or a spherical shape (semispherical shape), but in this embodiment, the end portion 137b is positioned on the distal end side and obliquely inward. A protruding piece formed by cutting and raising the wall of the protector 130 itself so as to protrude and presents a tongue-like nail. In addition, the convex part 137 is formed so that it may be located in the middle of each bus-line of the flow hole 135 provided in the trunk | drum 133, when the protector 130 is seen from the axis line O direction. That is, the flow hole 135 is opened with the direction of the one-dot chain line L in FIG. 7 as an axis. In the present embodiment, the protector that is the surrounding member is embodied in a cylindrical shape, but may be a rectangular tube shape.

  Thus, the protector 130 elastically deforms the convex portion 137 outward by externally fitting and pushing the base end portion of the body portion 133 into the small diameter cylindrical portion 121 on the distal end 125 side of the holder 120. It is configured to be fitted into the recess 124 in such a manner that its deformation is restored after being pushed in, and in the fitted state, the protector 130 is attached to the holder 120 so as not to be detached and to be non-rotatable around the axis O. It is configured. That is, as shown in FIG. 2 and FIG. 6, the protector 130 is attached by fitting the inner periphery on the opening side to the outer periphery of the small-diameter cylindrical portion 121 of the holder 120 simply by pushing it in. The efficiency is improved while simplifying and speeding up the work. Moreover, after the attachment, the protector 130 is not separated from the holder 120 even if the fitting is a clearance fit (slack fit), and thereafter, the handling of the intermediate assembly is facilitated. Can do. By attaching the protector 130 to the holder 120 in this way, the ceramic heater 110 whose heating resistor 114 side is exposed from the holder 120 is accommodated in the protector 130.

  In this embodiment, in such an attached state, the flow hole 135 of the body portion 133 does not face the substrate surface of the ceramic heater 110 and always faces at an angle of 45 degrees by the anti-rotation action of the convex portion 137. ing. Accordingly, when the sensor 100 is immersed and used, even if the liquid fills the protector 130 from the flow hole 135, the liquid may flow violently and collide with the substrate surface (main surface) of the ceramic heater 110. The collision is not a frontal collision. Therefore, since the impact can be mitigated, an undesired sudden change in heat can be prevented, thereby preventing measurement accuracy from being lowered. In this embodiment, they are opposed to each other at an angle of 45 degrees. However, if the flow holes 135 are provided so as to prevent the frontal collision of the liquid against the element, such an effect is expected. In the present embodiment, as described above, the tip 11 of the outer cylinder electrode 10 is extended to the tip of the axis O direction so as to surround the protector 130. Covered with For this reason, it can further reduce that the pressure accompanying a flow reaches a liquid property detection element directly. In this embodiment, the surrounding member is embodied as a cylindrical protector made of a metal plate, and a through hole is opened in the trunk portion, etc., but depending on the size of the mesh, for example, from a mesh plate to a bottomed cylindrical shape. Then, you may form in a monkey structure. In such a case, the mesh becomes a flow hole.

  The liquid property detection unit 30 having such a configuration is connected to the level detection unit 70 in an insulated state by attaching the holder 120 to the distal end portion 21 of the internal electrode 20. As shown in FIG. 2, the liquid property detection unit 30 is made of a rubber ring-shaped member interposed between the inner side of the outer cylindrical electrode 10 and the outer side of the inner electrode 20 together with the tip portion 21 of the inner electrode 20. The rubber bush 80, which is a support member, is positioned and supported in the outer cylinder electrode 10. However, in this embodiment, the rubber bush 80 has a portion corresponding to the convex portion 137 in the outer peripheral surface of the body portion 133 of the protector 130 and an outer peripheral surface of the large-diameter cylindrical portion 122 of the holder 120 in the axis O direction. It is configured to be attached to the outer peripheral surfaces of the body portion 133 and the large-diameter cylindrical portion 122 in an interference fit manner so as to straddle the front and rear. Although details will be described later, even if the fitting of the protector 130 to the holder 120 is a clearance fit, the protector 130 is firmly and stably attached to the holder 120 by the rubber bush 80 without rattling. It is configured as follows. Note that when the fitting of the protector 130 to the holder 120 is an interference fit, a stronger and more stable attachment can be obtained.

  The rubber bush 80, which is a support member used in this embodiment, is configured as follows. That is, as shown in FIGS. 8 to 11, the rubber bush 80 has a cylindrical shape, and each opening of the outer cylinder electrode 10 is formed on three outer peripheral lines 89 on the outer peripheral surface 89 that are equally spaced in the circumferential direction. Protrusions 87 that are respectively engaged with the portions 16 and function as prevention of removal and prevention of rotation are provided. Further, a plurality of (five in the present embodiment) groove portions 88 are provided along the axis O direction between the protrusions 87 in the circumferential direction of the outer peripheral surface 89.

  Further, the inner peripheral surface of the rubber bush 80 includes two inner peripheral surfaces 81 and 82 having different inner diameters formed so that the outer peripheral surface of the holder 120 is engaged, and a tapered inner peripheral surface connecting the two. 83. Then, on the inner peripheral surfaces 81 to 83, the positions corresponding to the respective buses on the outer peripheral surface 89 on which the protrusions 87 are formed are respectively arranged from the small-diameter inner peripheral surface 81 side to the large-diameter inner peripheral surface 82 side. Groove portions 84 that are continuous on the inner peripheral surfaces 81, 83, and 82 are respectively provided. The formation part of the small-diameter inner peripheral surface 81 of the rubber bush 80 is formed thicker than the formation part of the large-diameter inner peripheral surface 82.

  Further, as described above, the internal electrode 20 is pressed toward the front end side in the direction of the axis O by the two pressing plates 56 and 57 through the pipe guide 55 (see FIG. 1). As a result, as shown in FIG. 2, the stepped portion 123 of the holder 120 attached to the tip 21 of the internal electrode 20 is pressed against the inner peripheral surface 83 of the rubber bush 80. The holder 120 and the internal electrode 20 are elastically supported on the inner side of the outer cylinder electrode 10 by the rubber bush 80 positioned and held on the outer cylinder electrode 10.

  When such a liquid state detection sensor 100 is attached to a urea water tank (not shown) and used, as shown in FIG. 2, the outer cylinder electrode 10 has a distal end side in the direction of the axis O with respect to the rubber bush 80. The urea aqueous solution flows into the B portion and the C portion on the rear end side through the opening and the slit 15 at the most distal portion in the axis O direction of the outer cylinder electrode 10. In addition, the aqueous urea solution flows into part D in the protector 130 from part B via the liquid circulation holes 135 and 136. Then, the urea aqueous solution that has flowed into the B part and the C part passes through the flow path 85 formed by the groove part 88 of the rubber bush 80 and the inner peripheral surface of the outer cylinder electrode 10, and between the groove part 84 and the outer peripheral surface of the holder 120. It is circulated through the formed flow passage 86. Further, the flow passage 86 is continuous with the liquid circulation hole 135 (see FIGS. 4 to 6) of the protector 130 arranged so as to be aligned with the formation position of the groove 84 (see FIG. 12). Accordingly, the urea aqueous solution is circulated between the B part and the C part and between the D part and the C part via the flow passages 85 and 86. In addition, when an empty urea water tank is filled with a urea aqueous solution, there is a possibility that air may remain in the B part and the D part, but this air can reach the C part through the flow passages 85 and 86.

  Next, the principle of detecting the level and concentration of the aqueous urea solution by the liquid state detection sensor 100 of the present embodiment will be described. First, the principle of detecting the level of the urea aqueous solution in the level detection unit 70 will be described with reference to FIG. FIG. 13 is an enlarged cross-sectional view of the vicinity of the water surface of the urea aqueous solution filled in the gap between the outer cylinder electrode 10 and the inner electrode 20.

  The liquid state detection sensor 100 is assembled in a urea water tank (not shown) containing a urea aqueous solution with the front end side of the outer cylinder electrode 10 and the internal electrode 20 facing the bottom wall side. That is, the level detection unit 70 of the liquid state detection sensor 100 sets the direction of displacement of the urea aqueous solution whose volume changes in the urea water tank (not shown) as the axis O direction, and the outer cylinder electrode 10. In addition, the internal electrode 20 is assembled to a urea water tank (not shown) so that the tip side of the internal electrode 20 is a side (low level side) with a small capacity of the urea aqueous solution. And the electrostatic capacitance between the gaps of the outer cylinder electrode 10 and the inner electrode 20 is measured, and it is detected to what level the urea aqueous solution existing between the two is present in the axis O direction. As is well known, this is based on the fact that the capacitance increases as the difference in diameter between two points having different potentials in the radial direction decreases.

  That is, as shown in FIG. 13, in the portion not filled with the urea aqueous solution, the distance of the portion where the potential difference occurs between the gaps is interposed between the inner peripheral surface of the outer cylinder electrode 10 and the insulating coating 23. This is the total distance (indicated by distance E) of the distance corresponding to the thickness of the air layer (indicated by distance F) and the distance corresponding to the thickness of the insulating coating 23 (indicated by distance G). On the other hand, in the portion filled with the urea aqueous solution, the potential difference between the gaps is such that the potential of the outer cylinder electrode 10 and the urea aqueous solution is almost equal because the urea aqueous solution exhibits conductivity. The distance G corresponds to a thickness of 23.

  In other words, the capacitance between the gaps in the portion that is not filled with the urea aqueous solution is that the distance between the electrodes is F and the capacitance between the capacitor using air as a dielectric (non-conductor) and the distance between the electrodes is It can be said that this is the combined capacitance of a capacitor in which a capacitor having the insulating coating 23 as a dielectric is connected in series with G. The capacitance between the gaps in the portion filled with the urea aqueous solution can be said to be the capacitance of a capacitor in which the distance between the electrodes is G and the insulating coating 23 is a dielectric. And the electrostatic capacitance of the capacitor | condenser which connected both in parallel will be measured as an electrostatic capacitance of the level detection part 70 whole.

  Here, since the distance F between the electrodes sandwiching the air layer is larger than the distance G between the electrodes sandwiching the insulating coating 23, the capacitance per unit between the electrodes using air as a dielectric is The capacitance per unit between the electrodes using the insulating coating 23 as a dielectric is smaller. For this reason, the change in the capacitance of the portion filled with the urea aqueous solution is larger than the change in the capacitance of the portion not filled with the urea aqueous solution. Is proportional to the level of the aqueous urea solution. In this embodiment, the level detection of the aqueous urea solution is performed by a level detection circuit including a microcomputer mounted on the circuit board 60, and the level information signal obtained by the level detection circuit is sent via the connector 62. It outputs to an external circuit (for example, ECU). The external circuit determines whether or not the level of the urea aqueous solution is appropriate based on the input level information signal, and appropriately performs a process of notifying the driver when it is not appropriate.

  Next, the principle of detecting the concentration of urea as a specific component contained in the urea aqueous solution in the ceramic heater 110 constituting the liquid property detection unit 30 will be described. In general, it is known that the thermal conductivity of a liquid varies depending on the concentration of a specific component contained in the liquid. That is, when a heating resistor is used and the surrounding liquid is heated for a certain period of time, the temperature increase rate differs for liquids having different concentrations. It is also known that when a constant current is passed through the heating resistor, the resistance value of the heating resistor increases in proportion to an increase in the temperature around the heating resistor. From this, when a heating resistor is used and the surrounding liquid is heated for a certain period of time, if the degree of change in the resistance value of the heating resistor is obtained, the degree of temperature change in the surrounding liquid is obtained, and the concentration of the liquid is determined. Obtainable.

  The liquid state detection sensor 100 according to the present embodiment is configured to flow a constant current through the heating resistor 114, and a detection voltage Vd corresponding to the magnitude of its own resistance value is applied to both ends of the heating resistor 114. appear. When the potential at one end of the heating resistor 114 is Pin and the potential at the other end of the heating resistor 114 is Pout, the detection voltage Vd is obtained by the difference between the potential Pin and the potential Pout. Specifically, first, the detection voltage Vd immediately after the start of energization of the heating resistor 114 is measured, and the detection voltage Vd is measured again after a certain time (for example, after 700 ms). Then, the concentration of the urea aqueous solution is determined using a table (not shown) created in advance by experiments or the like, using the difference value between the two detection voltages Vd as a parameter. In this embodiment, similarly to the level detection of the urea aqueous solution, the concentration detection (calculation) of the urea aqueous solution is performed by the concentration detection circuit including the microcomputer mounted on the circuit board 60, and is obtained by the concentration detection circuit. The obtained concentration information signal is output to an external circuit (for example, ECU) via the connector 62. The external circuit determines whether or not the concentration of the urea aqueous solution is within an appropriate range based on the input concentration information signal, and appropriately performs a process of notifying the driver when it is not within the appropriate range.

  Needless to say, the present invention can be modified in various ways. For example, like the holder 350 of the liquid state detection sensor 300 shown in FIG. 14, a seal is provided between the inner circumference of the tip 321 of the internal electrode 320 and the cylindrical part 352 of the holder 350 inserted into the tip 321. The water tightness inside the internal electrode 320 may be ensured by interposing the ring 340. In this case, the insulating coating 323 is formed so as to be folded back from the outer peripheral side to the inner peripheral side of the internal electrode 320 at the tip 321 of the internal electrode 320. If the insulating coating 323 is formed at least up to the position where the seal ring 340 is disposed on the inner peripheral side of the tip portion 321 of the internal electrode 320, the internal electrode 320 can be obtained even if the level detection unit 70 is immersed in the urea aqueous solution. Does not come into direct contact with the aqueous urea solution.

  In the present embodiment, the heat generating resistor 114 of the ceramic heater 110 and the lead portions 112 and 113 use the same material and have different pattern cross-sectional areas so that the heat generating resistor 114 generates heat mainly. However, each material may be different. In this embodiment, the resistance value of the heating resistor 114 of the ceramic heater 110 is used and the urea concentration in the urea aqueous solution is obtained by referring to the table. The concentration of the urea aqueous solution may be calculated by substituting it into the calculation formula.

  Moreover, although the groove parts 84 and 88 of the rubber bush 80 were provided in the shape of a groove on the inner peripheral side or the outer peripheral side of the rubber bush 80, they may be formed as through holes that penetrate the thick portion. Further, the rubber bush 80 may be formed by omitting any of the groove portions 84 and 88. Moreover, although the outer cylinder electrode 10 and the inner electrode 20 are cylindrical, they may be rectangular.

  Further, as the insulating film 23 formed on the internal electrode 20, a material that is not easily corroded in accordance with the characteristics of the liquid (for example, oxidation / reduction properties) may be selected. The insulating film was formed by dipping or electrostatic powder coating. However, if the air layer is not mixed with the internal electrodes, the insulating film can be formed using an insulating tube. Formation may be performed. Furthermore, without forming the level detection unit 70 by the outer cylinder electrode 10 and the inner electrode 20, both cylindrical members are simply used as positioning members for disposing the liquid liquid detection unit 30 at the target position of the urea water tank. In this way, the sensor can be embodied as a sensor that uses the ceramic heater 110 to measure only the concentration of the urea aqueous solution.

  As will be understood from the above, in the sensor of the present invention, the outer cylinder electrode 10 in the above embodiment is removed and, instead of the inner electrode 20, for example, a simple cylinder (shaft) or a measurement target site such as a tank. A member such as a base or a flange provided with attachment means directly or indirectly is used as a holder attachment member.For example, if the holder attachment member is a cylinder, the tip thereof is the same as in the above-described embodiment. The heater 110 is supported by attaching the holder 120 that holds the heater 110 in a state where the tip of the ceramic heater 110 that is a liquid property detection element protrudes from the tip of the ceramic heater 110, and the above-described implementation is performed on the holder. As in the embodiment, the present invention can be embodied by attaching a protector as an enclosing member.

FIG. 6 can be said to show a specific example of such a sensor. That is, instead of the internal electrode 20 in FIG. 6, when this is a simple holder mounting member without such an electrode function, a ceramic heater 110 is used to measure a liquid property such as the concentration of urea aqueous solution, The sensor according to claim 1 or 2 is embodied. Even in this case, in order to stabilize the attachment of the protector 130, the protector 130 is not externally fitted to the portion corresponding to the convex portion 137 in the outer peripheral surface of the protector 130 and the outer peripheral surface of the holder 120. As shown by a two-dot chain line in FIG. 6, the support member 80 made of rubber and having a ring shape is tightly fitted to the outer peripheral surface of the protector 130 and the holder 120 so as to straddle the part. Install. The support member used in such a case only needs to be able to firmly fix the protector 130 to the holder 120, and therefore the cross-sectional shape (particularly the outer peripheral surface) may be embodied as an appropriate shape. What is necessary is just to set it as the rubber ring which has a suitable cross-sectional shape according to the shape of the protector 130 and the holder 120. FIG.

  Furthermore, the ceramic heater 110 as a liquid property detecting element may be used for detecting detection of the temperature of the liquid or the lower limit level of the liquid in addition to detecting the concentration of a specific component (for example, urea) contained in the liquid. . For example, when the temperature of the liquid is detected by the ceramic heater 110, the resistance value of the heating resistor 114 immediately after the constant current starts to flow through the heating resistor 114 (more specifically, the heating resistor 114), the temperature of the liquid can be detected. Since the resistance value immediately after the heating resistor 114 is energized shows a value corresponding to the temperature of the liquid, the temperature of the liquid can be detected by such a method. Further, the change behavior of the resistance value of the heating resistor 114 is greatly different between the case where the liquid is present around the ceramic heater 110 and the case where the liquid is not present. Detection may be performed.

The longitudinal section front view of a liquid state detection sensor. The expanded sectional view near the liquid property detection part of a liquid state detection sensor, and the further enlarged view of the principal part. The schematic diagram which shows the heater pattern of a ceramic heater. The perspective view which looked at the holder which protrudes and hold | maintains the front-end | tip of a ceramic heater from the front end side, and the perspective view which looked at the protector attached to this from the front end side. The fracture | rupture front view of the state which attached the holder which protrudes and hold | maintains the front-end | tip of a ceramic heater to the internal electrode, and the fracture | rupture front view of the protector attached to this. The fracture | rupture front view of the state which externally fitted and attached the protector in the site | part near the front-end | tip of a holder in FIG. X1-X1 sectional drawing in FIG. The perspective view which looked at the rubber bush from diagonally downward. The side view of a rubber bush. The top view of a rubber bush. Sectional drawing of the rubber bush seen from the arrow direction in the dashed-dotted line AA of FIG. The bottom view of the liquid state detection sensor which looked at the liquid state detection sensor shown in FIG. 1 in the axis line O direction from the front end side. The expanded sectional view of the water surface vicinity of the urea aqueous solution with which it filled between the gaps of an outer cylinder electrode and an internal electrode. The expanded sectional view of the liquid property detection part vicinity of the liquid state detection sensor as a modification.

10 Outer cylinder electrode (first member)
11 End portion 20 of outer cylinder electrode Internal electrode (second member, holder mounting member)
21 Front end portion 23 of internal electrode Insulating coating 30 Liquid property detection unit 70 Level detection unit 80 Rubber bush (support member)
100 Liquid state detection sensor 110 Ceramic heater (liquid property detection element)
110b Ceramic heater tip 114 Heating resistor 120 Holder 124 Holder recess 125 Holder tip 130 Protector (enclosing member)
135, 136 Flow hole 137 Convex part 137b End part of convex part itself

Claims (6)

A liquid state detection sensor comprising a liquid property detection element for detecting at least the concentration of a specific component in a liquid stored in a storage container,
A holder that holds the liquid property detection element in a state in which the tip of the liquid property detection element protrudes from its tip, a holder attachment member that supports the liquid property detection element by attaching the holder,
An enclosing member formed with a flow hole through which the liquid flows, and is attached to the front end portion or a portion near the front end of the holder so as to surround the front end portion of the liquid property detecting element. ,
The holder has a recess formed on the outer peripheral surface of the distal end portion or a portion near the distal end, while the surrounding member protrudes inward to a proximal end portion or a proximal end portion fitted on the holder. A convex part that can be fitted into the concave part by elastic deformation is provided, the convex part is fitted into the concave part, and the surrounding member is attached to the holder in a retaining shape , and the enclosure A support member that is made of rubber and has a ring shape so as to straddle a portion corresponding to the convex portion of the outer peripheral surface of the member and a portion of the outer peripheral surface of the holder where the surrounding member is not externally fitted. A liquid state detection sensor, wherein the sensor is attached to the outer peripheral surfaces of the surrounding member and the holder in an interference fit .   The convex portion is a projecting piece formed by cutting and raising the wall of the surrounding member so that the end portion of the convex portion itself is located on the tip side and projects obliquely inward. The liquid state detection sensor according to claim 1. A liquid state detection sensor comprising a liquid property detection element for detecting at least the concentration of a specific component in a liquid stored in a storage container,
A cylindrical first member extending in the longitudinal direction;
A cylindrical or solid second member that is disposed inside the first member and extends along the longitudinal direction of the first member;
Holding the liquid property detection element in a state where the tip of the liquid property detection element protrudes from its own tip, and a holder attached to the tip of the second member;
A flow hole through which the liquid flows is formed, and an enclosing member covering a radial periphery of the tip portion of the liquid property detection element protruding from the tip of the holder,
The holder has a recess formed on the outer peripheral surface of the distal end portion or a portion near the distal end, while the surrounding member protrudes inward to a proximal end portion or a proximal end portion fitted on the holder. It is provided with a convex part that can be fitted into the concave part by elastic deformation, the convex part is fitted into the concave part, and the surrounding member is attached to the holder in a retaining shape,
Between the outer side of the second member and the inner side of the first member, a rubber-made support member that supports the second member with respect to the first member is interposed, and the support The member straddles the surrounding member and the surrounding member so as to straddle the portion corresponding to the convex portion of the outer peripheral surface of the surrounding member and the portion of the outer peripheral surface of the holder where the surrounding member is not externally fitted. A liquid state detection sensor, wherein the liquid state detection sensor is attached to an outer peripheral surface of the holder in an interference fit. The convex portion is a projecting piece formed by cutting and raising the wall of the surrounding member so that the end portion of the convex portion itself is located on the tip side and projects obliquely inward. The liquid state detection sensor according to claim 3 . The liquid state detection sensor according to any one of claims 3 and 4 ,
The liquid state detection sensor according to claim 1, wherein a distal end portion of the first member extends to a position covering a circumference of the surrounding member in a radial direction. The liquid state detection sensor according to any one of claims 3 to 5 ,
The first member is an outer cylindrical electrode made of a conductor, while the second member is an inner electrode made of a conductor, and is housed in the housing container by the first member and the second member. A liquid state detection sensor, comprising: a level detection unit whose capacitance changes in accordance with a liquid level.

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